public class PeakIndexInAMountainArray {
    // 山峰数组的封顶索引 https://leetcode.cn/problems/peak-index-in-a-mountain-array/
    public int peakIndexInMountainArray(int[] arr) {
        int left=0,right=arr.length-1;
        while(left<right) {
            int mid=left+(right-left+1)/2;
            if(arr[mid]>arr[mid-1]) {
                left=mid;
            } else {
                right=mid-1;
            }
        }
        return left;
    }
}
